In the aforementioned three-dimensional shaping method, it is currently impossible to completely prevent sintering defects, due to the following reasons:
A. A problem with the control system involved in irradiating the laser beam or electron beam onto the powder layer may result in an excess or insufficiency of the supplied beam, forming a non-flat sintering surface with a generally regular uneven condition, compared to when each beam is supplied normally,
B. Due to formation of the uneven condition of above A or infiltration of chips, during formation of the powder layer, squeegee movement is hampered and it becomes difficult to achieve a uniform flat surface, or joining between the previously sintered layer and the newly sintered layer by melting may be incomplete, causing abnormalities in the powder layer surface that result in a non-flat powder layer surface with an irregular uneven condition.
However, since in a three-dimensional shaping method the laminating and sintering steps are repeated in a sealed apparatus, it is unavoidable that such sintering defects as mentioned in above A and B will be overlooked and only noticed after completion of all of the laminating steps and all of the sintering steps that have been repeated.
When a laser beam or electron beam has been irradiated onto the powder layer surface, sparks are constantly generated as the powder flies off (sputtering), as shown in FIG. 7.
When a sintering defect has occurred according to above A or B, the sparks are known to exhibit a pattern different from normal sintering, as an empirical rule.
In the prior art, however, the technical concept of focusing on the sparks generated during sintering to detect sintering defects has not been disclosed in any way.
Incidentally, in Patent Document 1, the sparks that are generated as powder flies off during three-dimensional shaping are merely considered to be a cause of abnormal shaping.
Moreover, no publicly known technical publications other than Patent Document 1 can be found that focus on the sparks generated during irradiation with different beams and that attempt to actively make use of those sparks in three-dimensional shaping.